An MRI apparatus utilizes a nuclear magnetic resonance phenomenon to create an image from any cross section traversing a subject. Specifically, such an MRI apparatus applies an RF magnetic field to a subject placed in a spatially homogeneous magnetic field (static magnetic field), causing nuclear magnetic resonance to occur, detects nuclear magnetic resonance signals being generated, and performs an imaging process on the signals thus detected, whereby a tomographic image is acquired.
A device that applies the RF magnetic field to the subject, and detects the nuclear magnetic resonance signals generated from the subject, is referred to as a radio frequency coil (hereinafter, referred to as an RF coil). The RF coil is provided with a loop unit (coil loop) for performing application and detection of the RF magnetic field. The smaller is the coil loop, the higher is the sensitivity of the coil, though its sensitivity region becomes narrower. On the other hand, when the coil loop is made larger, the sensitivity region can be expanded. Accordingly, in the RF coil, there are tradeoffs between the sensitivity level and the size of the sensitivity region. In addition, since the nuclear magnetic resonance signals are rotating-magnetic-field signals that are generated in the direction vertical to the static magnetic field, it is preferable to place the RF coil in the orientation allowing application and detection of the magnetic field to be vertical to the static magnetic field.
As discussed above, the sensitivity of the RF coil is enhanced with reduction of the size thereof, whereas the sensitivity region becomes narrower. As a technique to solve this problem, there is disclosed a multichannel array coil comprising RF coils small in diameter with high sensitivity, arranged in arrays (see Non Patent Document 1, for example). Since the multichannel array coil is high in sensitivity and provided with a wide sensitivity region, allowing acquisition of an image with a high SNR (Signal to Noise Ratio), currently, it serves as a dominating receiver RF coil. In the following description, each of the RF coils constituting the multichannel array coil will be referred to as a subcoil.
In general, when the RF coils having the same resonance characteristics are placed adjacent to each other, they interfere with each other due to magnetic coupling. Since performance of the RF coil is deteriorated due to the magnetic coupling, it is imperative to remove the magnetic coupling between the subcoils in the multichannel array coil. The Non Patent Document 1 discloses that the adjacent subcoils are placed in a manner that a part of the coil loop overlaps on another coil loop, thereby minimizing the magnetic coupling. Furthermore, a low-input preamplifier, an inductor, and a capacitor are used, so as to render a part of the coil loop to be high impedance, and interference from anything other than the subcoils can be reduced.
The Patent Document 1 and the Patent Document 2 disclose techniques where a decoupling means is provided in a multichannel coil, whereby magnetic coupling between the subcoils constituting the multichannel coil is reduced.